Fluidized bed reactors are known in the art. In particular, it is known to use fluidized beds for the combustion of dirty solid fuels, such as coal. During combustion, the fluidized bed reactor also suppresses toxic emissions by oxidizing burnable components of the fuel. For instance, limestone in the fluidized bed reacts with sulfur compounds in the fuel to generate calcium sulfate and thereby prevent the emission of SO.sub.x into the atmosphere.
U.S Pat. No. 4,843,981 (the '981 patent) discloses a fluidized bed reactor which recirculates a dense cloud of fine particulate. The cloud of particulate results in particle gas contact above the bed and thereby suppresses SO.sub.x emissions.
The '981 patent also teaches the injection of ammonia into the recycle cyclones of the reactor to suppress NO.sub.x emissions. This combustor has resulted in a clean burning low SO.sub.x and low NO.sub.x combustion system for solid fuel fired boilers and pressurized air heaters burning coal, coke, coal waste, petroleum coke, etc.
These prior art reactors have demonstrated the ability to operate at NO.sub.x and SO.sub.x emissions below 0.04 lbs/million BTU, with coke and coal fuels containing fuel bound nitrogen levels up to 2.5% and fuel bound sulfur of up to 3%. In these boiler and air heating applications, the fluid beds are operated as combustors to release energy to heat steam or compressed air by extracting energy from the fluid bed and the hot exhaust gas as required.
Pending U.S. patent application Ser. No. 07/672,067, filed Mar. 18, 1991, and assigned to the assignee of the present invention, discloses the concept of using a recirculating fluid bed reactor to clean the hot gas from a high temperature slagging coal combustor. The dirty gas from the combustor is passed through the freeboard of the reactor. The excess heat from the bed of the reactor is used to preheat the air upstream of the slagging combustor. Conditions in the fluid bed rector were optimized to clean the gas for the thermodynamic cycle described.